Soul Eater primarily revolves around students classified as meister at the Shibusen, which is a school located in the fictional Death City. The school is run by Shinigami, the God of Death himself, as a training facility for weapons and the human wielders of those weapons, the meisters. Shinigami created the school as an organization that enforces peace in order to prevent the rebirth of the "kishin" , the evil demon god. The ultimate goal of the students with their weapons is to have their weapons defeat and absorb the souls of ninety-nine evil humans and one witch, in order to become a weapon usable by Shinigami.
But this main plot gets neglected in the anime, which turns into a showdown between the dark forces of the witch Arachne who got a hold of the reborn Kishin, which Shibusen wants to get back. I pretty much like the story, and the characters are amazing. So just READ it^^